The invention relates to polyurethanes and more particularly to a thermoplastic molding composition containing a resinous blend of polyurethane and a polyolefin.
A thermoplastic polyurethane resin which is prepared by reacting an isocyanate, a polyol and a reactive polyolefin, and a chain extender, is disclosed. It was surprisingly and unexpectedly found that the inventive resin forms compatible blends with polyolefins.
Conventional thermoplastic polyurethane resins are the reaction product of a diisocyanate, a chain extender (a short chain diol) and a polyol. It has long been recognized that such polyurethane resins are incompatible with, and hence not easily blended with, polyolefins such as polyethylene and polypropylene. This incompatibility results in inhomo-geneous blends which tend to delaminate and often feature poor mechanical properties.
U.S. Pat. No. 4,883,837 and the document mentioned there as prior art reflect the many attempts to make compatible blends of polyolefins with thermoplastic polyurethane. Note may also be made of U.S. Pat. No. 4,752,626 which disclosed a polyisocyanate prepared from a polyol blend containing polyolefinic polyol. A polyolefin diol was referred to in U.S. Pat. No. 5,332,786 as a reactant with diisocyanate in the preparation of an adhesive.
The reactants necessary in the preparation of the thermoplastic polyurethane resin of the present invention comprise
(i) at least one member selected from among aliphatic and aromatic isocyanates, and
(ii) at least one polymeric polyol, most preferably a member selected from between polyester polyol and polyether polyol, and
(iii) a reactive polyolefin which contains at least one member selected from hydroxyl, amine and carboxylic acid functional groups, and
(iv) a chain extender.
Importantly, the amount of said (iii) is at least 1.0 equivalent %, preferably at least 8 equivalent %, relative to the amount of said (ii) and the ratio of said isocyanate equivalents to equivalents of active hydrogen-containing materials is within the range of 0.90:1 to 1.10:1, and preferably, 0.95:1 to 1.05:1.
The chain extender suitable in the present context is a C2-10 hydrocarbon compound having an isocyanate-reactive chain termination. In a preferred embodiment of the invention, the chain extender is hydroxy and/or an amine terminated. In a further embodiment of the invention, additional polyols may be included as reactants.
An additional embodiment of the invention relates to a thermo-plastic composition containing a blend of the polyurethane of the invention and polyolefin resin. The polyurethane of the invention was found to be more compatible with polyolefin than other prior art polyurethanes.
The isocyanate suitable in the present invention is any of the organic isocyanates previously disclosed as suitable in the preparation of TPU resins, preferably diisocyanates, and include aliphatic, aromatic and cycloaliphatic diisocyanates, and mixtures thereof.
Illustrative isocyanates but non-limiting thereof are methylenebis(phenyl isocyanate) including the 4,4xe2x80x2-isomer, the 2,4xe2x80x2-isomer and mixtures thereof, m- and p-phenylene diisocyanates, chlorophenylene diisocyanates, a,axe2x80x2-xylylene diisocyanate, 2,4- and 2,6-toluene diisocyanate and the mixtures of these latter two isomers which are available commercially, tolidine diisocyanate, hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, isophorone diisocyanate and the like; cycloaliphatic diisocyanates such as methylenebis(cyclohexyl isocyanate) including the 4,4xe2x80x2-isomer, the 2,4xe2x80x2-isomer and mixtures thereof, and all the geometric isomers thereof including trans/trans, cis/trans, cis/cis and mixtures thereof, cyclohexylene diisocyanates (1,2-; 1,3-; or 1,4-, 1-methyl-2,5-cyclohexylene diisocyanate, 1-methyl-2,4-cyclohexylene diisocyanate, 1-methyl-2,6-cyclohexylene diisocyanate, 4,4xe2x80x2-isopropylidenebis(cyclohexyl isocyanate), 4,4xe2x80x2-diisocyanatodicyclohexyl, and all geometric isomers and mixtures thereof and the like. Also included are the modified forms of methylenebis(phenyl isocyanate). By the latter are meant those forms of methylenebis(phenyl isocyanate) which have been treated to render them stable liquids at ambient temperature (circa 20xc2x0 C.). Such products include those which have been reacted with a minor amount (up to about 0.2 equivalents per equivalent of polyisocyanate) of an aliphatic glycol or a mixture of aliphatic glycols such as the modified methylenebis(phenyl isocyanates) described in U.S. Pat. Nos. 3,394,164; 3,644,457; 3,883,571; 4,031,026; 4,118,411; and 4,299,347. The modified methylenebis(phenyl isocyanates) also include those which have been treated so as to convert a minor proportion of the diisocyanate to the corresponding carbodiimide which then interacts with further diisocyanate to form uretone-imine groups, the resulting product being a stable liquid at ambient temperatures as described, for example, in U.S. Pat. No. 3,384,653. Mixtures of any of the above-named isocyanates can be employed if desired.
Preferred classes of organic diisocyanates include the aromatic and cycloaliphatic diisocyanates. Preferred species within these classes are methylenebis(phenyl isocyanate) including the 4,4xe2x80x2-isomer, the 2,4xe2x80x2-isomer, and mixtures thereof, and methylenebis(cyclohexyl isocyanate) inclusive of the isomers described above.
The preferred isocyanates are methylene bis(phenyl isocyanate) and methylene bis(cyclohexyl isocyanate).
The polymeric diols suitable in the context of the invention are those conventionally employed in the art for the preparation of TPU resins. The formation of soft segments in the resulting polymer is attributed to the polymeric diols. Preferably, the polymeric diols have molecular weights (number average) within the range of 500 to 10,000, preferably 1000 to 4,000. Naturally, and often times advantageously, mixtures of such diols are also possible. Examples of the suitable diols include polyether diols, polyester diols, hydroxy-terminated polycarbonates, hydroxy-terminated copolymers of dialkyl siloxane and alkylene oxides such as ethylene oxide, propylene oxide and the like, and mixtures thereof.
Examples of suitable polyether polyols include polyoxyethylene glycols, polyoxypropylene glycols which, optionally, have been capped with ethylene oxide residues, random and block copolymers of ethylene oxide and propylene oxide; polytetramethylene glycol, random and block copolymers of tetrahydrofuran and ethylene oxide and/or propylene oxide. The preferred polyether polyols are random and block copolymers of ethylene and propylene oxide of functionality approximately 2.0 and polytetramethylene glycol polymers of functionality about 2.0.
The suitable polyester polyols include the ones which are prepared by polymerizing xcex5-caprolactone using an initiator such as ethylene glycol, ethanolamine and the like, and those prepared by esterification of polycarboxylic acids such as phthalic, terephthalic, succinic, glutaric, adipic, azelaic and the like acids with polyhydric alcohols such as ethylene glycol, butanediol, cyclohexane-dimethanol and the like. An example of a suitable polyester polyol is butanediol adipate.
Among the suitable amine-terminated polyethers, mention may be made of the aliphatic primary diamines structurally derived from polyoxypropylene glycols. Polyether diamines of this type are available under the trademark JEFFAMINE from Jefferson Chemical Company.
Examples of polycarbonates containing hydroxyl groups include those prepared by reaction of diols such as propane-1,3-diol, butane-1,4-diol, hexane-1,6-diol, 1,9-nonanediol, 2-methyloctane-1,8-diol, diethylene glycol, triethylene glycol, dipropylene glycol and the like with diaryl-carbonates such as diphenylcarbonate or with phosgene.
Examples of suitable silicon-containing polyethers include copolymers of alkylene oxides with dialkylsiloxanes such as dimethyl-siloxane and the like; other suitable silicon-containing polyethers have been disclosed in U.S. Pat. Nos. 4,057,595 and in 4,631,329 both of which documents are incorporated herein by reference.
Preferred diols are polyether diols and polyester diols as referred to above.
Suitable chain extenders which are used in the preparation of the polyurethane resin of the invention include any of those known in the TPU art disclosed above. Typically the extenders may be aliphatic straight and branched chain diols having from 2 to 10 carbon atoms, inclusive, in the chain. Examples of suitable diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, and the like; 1,4-cyclohexanedimethanol; hydroquinone-bis-(hydroxyethyl)ether; cyclohexylenediols (1,4-, 1,3-, and 1,2-isomers), isopropylidenebis(cyclohexanols); diethylene glycol, dipropylene glycol, ethanolamine, N-methyldiethanolamine, and the like; and mixtures of any of the above. Minor proportions (less than about 20 equivalent percent) of the difunctional extender may be replaced by trifunctional extenders and/or monofunctional extenders, without adversely effecting the thermoplasticity of the resulting TPU resin; illustrative of such extenders are glycerol, trimethylolpropane, and 1-octadecanol and the like.
While any of the diol extenders described and exemplified above can be employed alone, or in admixture, it is preferred to use 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, ethylene glycol, and diethylene glycol, either alone or in admixture with each other or with one or more of the aliphatic diols which were named previously. Particularly preferred diols are 1,4-butanediol, 1,6-hexanediol and 1,4-cyclohexanedimethanol.
The equivalent proportions of polymeric diol to said extender may vary considerably depending on the desired hardness for the TPU resin. In general, the proportions fall within the range of from about 1:1 to about 1:20, preferably from about 1:2 to about 1:10. At the same time, the overall ratio of isocyanate equivalents to equivalents of active hydrogen containing materials is within the range of 0.90:1 to 1.10:1, and preferably, 0.95:1 to 1.05:1.
The reactive polyolefin suitable in the context of the invention contains at least one member selected from hydroxyl, amine and carboxylic acid functional groups. Preferably, the reactive polyolefin is a reactive poly(ethylene/butylene)copolymer. Most preferably the reactive polyolefin conforms to 
where X denotes an isocyanate-reactive group selected from among hydroxyl, amine and carboxylic acid functional groups, and where m is about 0 to 550, preferably 0 to 220 and n is about 0 to 270, preferably 110 to 0 and the number average molecular weight of the copolymer is about 500 to 15,000, preferably 1,000 to 6,000 g/mol and its functionality is in the range of about 1.7 to 2.5, preferably about 2.0.
The preferred reactive polyolefin is hydroxyl terminated poly(ethylene/butylene) copolymer having a molecular weight of about 4400 g/mol. Such copolymer is available commercially from Shell as Kraton HPVM2201.
The preparation of the TPU resin of the invention follows procedures and methods which are conventional and which are well known to the art-skilled. If desired, the polyurethanes can have incorporated in them, at any appropriate stage of preparation, additives such as pigments, fillers, lubricants, stabilizers, antioxidants, coloring agents, fire retardants, and the like, which are commonly used in conjunction with polyurethane elastomers.
It is frequently desirable, but not essential, to include a catalyst in the reaction mixture employed to prepare the thermoplastic resin of the invention. Any of the catalysts conventionally employed in the art to catalyze the reaction of an isocyanate with a reactive hydrogen containing compound can be employed for this purpose; see, for example, Saunders et al., Polyurethanes, Chemistry and Technology, Part I, Interscience, New York, 1963, pages 228-232; see also, Britain et al., J. Applied Polymer Science 4, 207-211, 1960. Such catalysts include organic and inorganic acid salts of, and organometallic derivatives of bismuth, lead, tin, iron, antimony, uranium, cadmium, cobalt, thorium, aluminum, mercury, zinc, nickel, cerium, molybdenum, vanadium, copper, manganese and zirconium, as well as phosphines and tertiary organic amines. Representative organotin catalysts are stannous octoate, stannous oleate, dibutyltin dioctoate, dibutyltin dilaurate, and the like. Representative tertiary organic amine catalysts are triethylamine, triethylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-ethylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetraethylethylenediamine, N-methylmorpholine, N-ethylmorpholine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylguanidine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,3-butanediamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, and the like. The amount of catalyst employed is generally within the range of about 0.02 to about 2.0 percent by weight based on the total weight of the reactants.
The thermoplastic composition of the invention comprises a blend containing about 1 to 99, preferably about 40 to 80 wt % of the thermoplastic polyurethane resin described above and a complementary amount of polyolefin. The polyolefin suitable in the context of the inventive blends is well known and readily available in commerce. Normally, the polyolefin has a weight average molecular weight of about 50,000 to 2,000,000, preferably 200,000 to 1,000,000. Among the suitable polyolefins, mention may be made of polyethylene, polypropylene, polybutadiene and polybutylene. The preferred polyolefin is LDPE.
The preparation of the composition of the invention follows conventional means and procedures which are well known in the art.